Effects of anisomycin on consolidation and reconsolidation of a morphine-conditioned place preference

Protein synthesis inhibitors block consolidation of memory and may also block the reconsolidation of a reactivated memory in paradigms of aversive learning, but the evidence for reconsolidation effects is conflicting in appetitive paradigms. We now report that intra-cerebroventricular (ICV) anisomycin (400 μg) prevents consolidation of morphine-induced place preference (CPP), but does not impair its reconsolidation unless the reactivation procedure associates anisomycin with the morphine context. Rats were injected alternately with morphine (5 mg/kg, IP) or vehicle, and confined to one of two distinctive compartments in a three compartment apparatus. On a subsequent day rats were allowed to choose the compartment they preferred in a 20 min test session. In the first experiment, rats that were injected with vehicle or with anisomycin before or 3 h after training sessions, developed a CPP. However, rats that received anisomycin ICV immediately after training sessions did not develop a CPP. In experiment 2, rats received no ICV injections during initial training. Once a CPP was established, they received four additional training sessions on which they received vehicle or anisomycin ICV. All groups continued to prefer the morphine-paired compartment after reactivation sessions with vehicle or anisomycin ICV. In experiment 3, ICV anisomycin was administered selectively on morphine-paired reactivation trials or saline-paired reactivation trials and the CPP was weakened or strengthened, respectively. This suggests that associations between aversive effects of the amnestic treatment and the morphine context might mimic disruption of reconsolidation.